There's info on initial fill after evacuation & vacuum testing if you scroll far enough under Step 7 in this article: https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

 

thank you. is there some diagram about the ac relay and how to test it?

There's info on initial fill after evacuation & vacuum testing if you scroll far enough under Step 7 in this article: https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

 

You won't have power reaching the coil in the relay until the system pressure sensor says there's enough pressure. Step 7 in the article shows how to force sufficient pressure into the system to make the pressure sensor happy.

If you suspect the relay for reasons other than an under-pressured system, it's a common failure and a relatively inexpensive part. Buy it locally and if it doesn't fix things, take it back for a refund and put back the one you have.

OR

Just follow common relay test procedures:

 

The AC relay seemed fine. Bypassing it, AC clutch engaged. Keeping the AC clutch engaged for 10 minutes, the refrigerant still couldn't go in.


The low pressure readed -30. The high pressure readed 0. Does this mean the AC compressor is ok but AC system is leaking somewhere?


Thanks.

You won't have power reaching the coil in the relay until the system pressure sensor says there's enough pressure. Step 7 in the article shows how to force sufficient pressure into the system to make the pressure sensor happy.

If you suspect the relay for reasons other than an under-pressured system, it's a common failure and a relatively inexpensive part. Buy it locally and if it doesn't fix things, take it back for a refund and put back the one you have.

OR

Just follow common relay test procedures: https://www.youtube.com/watch?v=IpRWcNoLdwQ

 

Yes to above links.

Once vacuum has been drawn down for AT LEAST 30 minutes and the pump turned off, the vacuum will allow refrigerant to be forced into the system without the compressor running, in fact the engine does not need to be on.

The important parts are you need to know how much (by weight) the system is designed to hold. Then weigh the cans as they are emptied into the system. Once the system pressure is balanced after dumping the initial can, there should be enough pressure to cancel the low pressure switch and turn the compressor on for continued filling.

 

Sounds like you have a blockage in the system, that's moving somewhat under charging and behaving like a primer pump (which is why you're getting the readings you are). I'd overhaul the A/C system, flush if you want, or get good A/C components from junkyard cars and swap out the whole system. And make sure there is the proper amount and viscosity of PAG oil before recharging, or take it to a shop with a machine that will autoinject the correct amount.

 

what I observed is below
1) bypassing the AC relay, ac clutch began spinning, low pressure gauge read -30psi, but only 1oz refrigerant was drawn in. When stop bypassing the AC relay, low pressure gauge went to 15psi. When closing the refrigerant, the low pressure gauge went to 0psi.
2) when vacuuming the AC system for about 15 minutes, low pressure gauge read -15 psi or so. When stopping vacuuming, the reading went to 0 immediately.


My question is
does the AC system have a blockage or leaking or both?
does the observation 1 mean AC compressor works well?
does the observation 2 mean there is a serious leaking in the AC system?


Thank you.

 

Re: 2
One thought occurred to me -- the check valve in your vacuum pump might be bad. Try drawing a vacuum, then before you turn off the pump, close the valve on the vacuum/refrigerant line, THEN turn off the pump.

If your a/c system STILL drops to 0 immediately with that valve closed, insightbrewery is right, you should be able to hear the air being sucked into the system.

 

The last time I chased AC leak was with compressed air - cheaper and faster than wasting refrigerant . Your system is obviously empty. You'll need to make an adapter using and air fitting and hooking up an air compressor - if you have one of course. It will provide a constant flow and pressure to either hear leak and/or use soap solution to see bubbles.

If you can't do this then I'd take it to a pro.